Multi-metal oxide catalyst and method for producing (meth)acrylic acid by using the same

ABSTRACT

The present invention provides a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included); a method for producing (meth)acrylic acid from at least one reactant selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, in which a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included) is used as a catalyst; and a reactor used for producing (meth)acrylic acid from at least one reactant selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, in which a Mo—Bi—Nb based composite metal oxide (with the proviso that Te is not included) is used as a catalyst. Further, the present invention provides a method for producing the (meth)acrylic acid without any additional process of converting (meth)acrolein into (meth)acrylic acid.

This application is a divisional application of U.S. patent applicationSer. No. 12/309,648, filed on Jan. 26, 2009, which is a national stageapplication of International Application No. PCT/KR2007/003489, filed onJul. 19, 2007, which claims priority from Korea Patent Application No.10-2006-71061 filed on Jul. 27, 2006 in the KIPO, the entire contents ofwhich are fully incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a Mo—Bi—Nb based composite metaloxide(multi-metal oxide), and a method for producing (meth)acrylic acidfrom propylene or the like by using the Mo—Bi—Nb based composite metaloxide as a catalyst. Further, the present invention relates to a methodfor producing (meth)acrylic acid from propylene or the like by anone-step catalyst reaction.

BACKGROUND ART

A process for producing an unsaturated fatty acid from olefin by way ofan unsaturated aldehyde is a typical process of gas-phase catalyticoxidation.

Particular examples thereof include a process of producing (meth)acrylicacid from a staring material such as propylene, propane, isobutylene,t-butyl alcohol or methyl-t-butyl ether (referred to as ‘propylene orthe like’, hereinafter) by way of corresponding (meth)acrolein.

In this connection, in the first step of partially oxidizing olefins tounsaturated aldehyde, composite metal oxides containing molybdenum andbismuth are generally used as a catalyst. In the second step ofpartially oxidizing the unsaturated aldehyde, which is a main product ofthe first step, to unsaturated fatty acid, composite metal oxidescontaining molybdenum and vanadium are used as a catalyst.

More particularly, in the first step, propylene or the like is oxidizedby oxygen, inert gas for dilution, water steam and a certain amount of acatalyst, so as to produce (meth)acrolein as a main product. Then, inthe second step, the (meth) acrolein is oxidized by oxygen, inert gasfor dilution, water steam and a certain amount of a catalyst, so as toproduce (meth)acrylic acid. The catalyst used in the first step is aMo—Bi based multinary metal oxide, which oxidizes propylene or the liketo produce (meth)acrolein as a main product. Also, some (meth)acroleinis continuously oxidized on the same catalyst to partially produce(meth)acrylic acid. The catalyst used in the second step is a Mo—V basedmultinary metal oxide, which mainly oxidizes (meth)acrolein of the mixedgas containing the (meth)acrolein produced from the first step toproduce (meth)acrylic acid as a main product.

A reactor for performing the aforementioned process is provided eitherin such a manner that both the two-steps can be performed in one system,or in such a manner that the two steps can be performed in differentsystems.

As mentioned above, the first-step catalyst involved in gas-phasepartial oxidation using propylene or the like as a starting material isthe Mo—Bi based multinary metal oxide, with which (meth)acrolein isproduced as a main product and 10% or less of (meth)acrylic acid isproduced.

As disclosed in JP-A-8-3093, a conventional first-step catalyst is acomposite oxide represented by the formula ofMo_(a)—Bi_(b)—Fe_(c)—A_(d)—B_(e)—C_(f)-D_(g)-O_(x) (wherein Mo, Bi andFe represent molybdenum, bismuth and iron, respectively; A is nickeland/or cobalt; B is at least one element selected from the groupconsisting of manganese, zinc, calcium, magnesium, tin and lead; C is atleast one element selected from the group consisting of phosphorus,boron, arsenic, Group 6B elements in the Periodic Table, tungsten,antimony and silicon; D is at least one element selected from the groupconsisting of potassium, rubidium, cesium and thallium; when a=12,0<b≦10, 0<c≦10, 1≦d≦10, 0≦e≦10, 0≦f≦20, and 0<g≦2; and x is a valuedefined by the oxidation state of each element). When gas-phasecatalytic oxidation of propylene is performed with molecular oxygen byusing the first-step catalyst, and by operating the first-step catalystbed at a temperature of 325° C., acrolein is produced with a yield of81.3% and acrylic acid is produced with a yield of 11%. In other words,acrylic acid content is low in the reaction product obtained by usingthe first-step catalyst.

Meanwhile, JP-A-5-293389 discloses a catalyst represented by the formulaof Mo_(a)Bi_(b)Fe_(c)A_(d)X_(e)Y_(f)Z_(g)Si_(h)O_(i) (wherein Mo, Bi,Fe, Si, and O represent molybdenum, bismuth, iron, silicon and oxygen,respectively; A is at least one element selected from the groupconsisting of cobalt and nickel; X is at least one element selected fromthe group consisting of magnesium, zinc, manganese, calcium, chrome,niobium, silver, barium, tin, tantalum and lead; Y is at least oneelement selected from the group consisting of phosphorus, boron, sulfur,selenium, Group 6B elements in the Periodic Table, cerium, tungsten,antimony and titanium; Z is at least one element selected from the groupconsisting of lithium, sodium, potassium, rubidium, cesium and thallium;and each of a, b, c, d, e, f, g, h and i represents the atomic ratio ofeach element, with the proviso that when a=12, b=0.01 to 3, c=0.01 to 5,d=1 to 12, e=0 to 6, f=0 to 5, g=0.001 to 1, and h=0 to 20, and i is theoxygen atom number needed to satisfy the atomic valence of eachelement). When gas-phase catalytic oxidation of propylene is performedby using the above catalyst to produce acrolein and acrylic acid,acrylic acid is produced with a yield of 6.2 mole % under a propyleneconversion ratio of 99.1 mole % and an acrolein selectivity of 89.6 mole%. In other words, acrylic acid content is still low in the reactionproduct obtained by using the first-step catalyst.

Further, the known production process comprising the two-steps ofpartial oxidation requires a separate reactor or reaction zone in eachreaction step, and catalysts having different compositions are providedaccording to the requirements of each step. That is, hardware (physicaloperating system) should be controlled and supervised under the optimalreaction conditions, of which complexity gives troubles and difficultiesin operation.

DISCLOSURE Technical Problem

The present invention provides a catalyst capable of producing(meth)acrylic acid with high productivity, in which the above mentionedproblems are solved by using a simple and economical method, that is,one-step catalyst reaction.

Further, the present invention provides an one-step reaction process forstably producing (meth)acrylic acid at high yield over a long period oftime, in which problems such as a hotspot problematic in a typicalexothermic reaction, degradation and a reduction in yield due to thehotspot can be solved by packing of a desirable catalyst.

Technical Solution

The present invention provides a Mo—Bi—Nb based composite metal oxide(with the proviso that Te is not included).

Further, the present invention provides a process for producing(meth)acrylic acid using at least one reactant selected from the groupconsisting of propylene, propane, isobutylene, t-butyl alcohol andmethyl-t-butyl ether by using a Mo—Bi—Nb based composite metal oxide(with the proviso that Te is not included) as a catalyst.

Furthermore, the present invention provides a process for producing(meth)acrylic acid using at least one reactant selected from the groupconsisting of propylene, propane, isobutylene, t-butyl alcohol andmethyl-t-butyl ether by using a Mo—Bi—Nb based composite metal oxide asa catalyst, without any additional process of converting (meth)acroleininto (meth)acrylic acid.

Further, the present invention provides a reactor for producing(meth)acrylic acid using at least one reactant selected from the groupconsisting of propylene, propane, isobutylene, t-butyl alcohol andmethyl-t-butyl ether, in which a Mo—Bi—Nb based composite metal oxide isused as a catalyst.

Advantageous Effects

According to the present invention, when the first-step catalystcomprising a Mo—Bi—Nb based composite metal oxide as an essentialcomponent is only used in the production of (meth)acrylic acid usingpropylene or the like, yield and/or selectivity of (meth)acrylic acidincreases in the reaction products, and thus the second oxidation stepand a separate catalyst required for conversion of (meth)acrolein toacrylic acid in the conventional two-step process are not needed, andthe heat of formation is effectively controlled by packing of anefficient catalyst. As a result, (meth)acrylic acid can be stablyproduced with high yield for a long period of time.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating the structure of fluidized bedreactor capable of using a catalyst according to the present invention.

BEST MODE

Mo—Bi based first-step metal oxide catalysts for producing(meth)acrolein by oxidation of propylene or the like, which have beendisclosed to date, generally provide selectivity from propylene or thelike to (meth)acrolein and (meth)acrylic acid of about 90 mole % ormore, wherein the molar ratio of (meth)acrolein to (meth)acrylic acid inthe first-step reaction product is about 9:1. Additionally, when thefirst-step reaction product is subjected to the second-step reaction, itis possible to obtain a product comprising (meth)acrylic acid as a mainproduct from (meth)acrolein.

The present inventors have found that when a Mo—Bi based first-stepmetal oxide catalyst also containing Nb, that is, a Mo—Bi—Nb basedcomposite metal oxide is prepared and used as the first-step reactioncatalyst, (meth)acrylic acid is produced using propylene at yield of 60mole % or more by catalytic reaction during an one-step process.

Therefore, as compared to other Mo—Bi based metal oxides used as thefirst-step reaction catalyst in the conventional two-step reactionprocess, when the Mo—Bi—Nb based composite metal oxide according to thepresent invention is used as a catalyst, provided is higher selectivityof (meth)acrylic acid in the reaction products obtained by the catalyticreaction using the catalyst. As a result, the additional second step ofcatalytic reaction, in which (meth)acrolein is converted into(meth)acrylic acid, can be minimized or excluded. Accordingly, in thepresent invention, (meth)acrylic acid can be produced from propylene orthe like at high yield, by one-step process comprising a single seriesof catalyst or by a reaction comprising a minimized two-step catalystreaction, which is impossible with the conventional catalystcomposition.

(1) The Mo—Bi—Nb based composite metal oxide of the present invention ispreferably a composite metal oxide represented by the following Formula1.

Mo_(a)Bi_(b)Nb_(c)A_(d)B_(e)C_(f)D_(g)E_(h)F_(i)O_(j)  [Formula 1]

wherein Mo represents molybdenum, Bi represents bismuth, and Nbrepresents niobium;

A is at least one element selected from the group consisting of W, Sb,As, P, Sn and Pb;

B is at least one element selected from the group consisting of Fe, Zn,Cr, Mn, Cu, Pd, Ag and Ru;

C is at least one element selected from the group consisting of Co, Cd,Ta, Pt and Ni;

D is at least one element selected from the group consisting of Si, Al,Zr, V and Ce;

E is at least one element selected from the group consisting of Se, Ga,Ti, Ge, Rh and Au;

F is at least one element selected from the group consisting of Na, K,Li, Rb, Cs, Ca, Mg, Sr, Ba and MgO;

each of a, b, c, d, e, f, g, h, i, and j represents the atomic ratio ofeach element; and

when a=12, b is 0.01 to 20, c is 0.001 to 20, d is 0 to 15, e is 0 to20, f is 0 to 20, g is 0 to 10, h is 0 to 10, i is 0 to 10, and j is avalue defined by the oxidation state of each of the above elements.

When used as a catalyst, the Mo—Bi—Nb based composite metal oxideaccording to the present invention may be used alone or may be supportedon an inert carrier. Examples of the carrier include porous ornon-porous alumina, silica-alumina, silicon carbide, titanium dioxide,magnesium oxide, aluminum sponge, or the like. Additionally, the carriermay take a cylindrical shape, a hollow cylindrical shape, or a sphericalshape, but is not limited thereto. For example, a catalyst having acylindrical shape preferably has a ratio of length to diameter (outerdiameter) (L/D ratio) of 1 to 1.3, and more preferably has an L/D ratioof 1. A catalyst having a cylindrical or spherical shape preferably hasan outer diameter of 3 to 10 mm, more preferably of 4 to 8 mm.

The Mo—Bi—Nb based composite metal oxide according to the presentinvention may be prepared by a typical method for producing a compositemetal oxide, except that a different composition is used.

There is no particular limitation in the shape of a metal precursorforming the Mo—Bi—Nb based composite metal oxide. For example, acompound that is provided originally in the form of an oxide or can beconverted into an oxide by heating (i.e. calcination) at least in thepresence of oxygen, for example, halogenide, nitride, formate, oxalate,citrate, acetate, carbonate, amine complex, ammonium salt and/orhydroxide may be used as a starting material.

According to an embodiment of the present invention, the method forpreparing the composite metal oxide comprises the steps of: dissolvingor dispersing a predetermined amount (stoichiometric amount) of eachstarting material containing each element in an aqueous medium; heatingthe resultant solution or dispersion under stirring; allowing the systemto evaporate to obtain a dry solid and drying and pulverizing the solid;and molding the powder into a desired shape via extrusion molding toobtain tablets or granules. In this case, glass fibers and inorganicfibers including various kinds of whiskers, which are known to improvethe strength and frictional resistance, may be further added.Additionally, in order to control the properties of the catalyst forexcellent reproducibility, other additives known as powder binders, suchas ammonium nitrate, cellulose, starch, polyvinyl alcohol, stearic acid,or the like, may be used.

The composite metal oxide catalyst according to the present inventionmay be obtained by calcining the molded product or the product supportedon a carrier under a flow of 0.2 to 2 m/s at 200 to 600° C. for about 1to 10 hours or more. The calcination step may be performed under aninert gas atmosphere, an oxidative atmosphere, for example, air (amixture of inert gas and oxygen), or a reductive atmosphere (e.g., amixture of inert gas, oxygen and NH₃, CO and/or H₂). The calcinationstep may be performed over a period of several minutes to several hours,and the calcination period generally decreases as the temperatureincreases.

(2) The Mo—Bi—Nb based composite metal oxide according to the presentinvention may be used as a catalyst to produce (meth)acrylic acid fromat least one reactant selected from the group consisting of propylene,propane, isobutylene, t-butyl alcohol, and methyl-t-butyl ether.

In this case, among the reaction products obtained by catalytic actionof the Mo—Bi—Nb based composite metal oxide, (meth)acrylic acid isproduced at yield of 60 mole % or more.

Therefore, the Mo—Bi—Nb based composite metal oxide according to thepresent invention can be used as a catalyst producing (meth)acrylic acidfrom at least one reactant selected from the group consisting ofpropylene, propane, isobutylene, t-butyl alcohol and methyl-t-butylether, without any additional process of converting (meth)acrolein into(meth)acrylic acid.

Particularly, the Mo—Bi—Nb based composite metal oxide according to thepresent invention may be used as a catalyst for the first-step partialoxidation in a process for producing (meth)acrylic acid, the processcomprising a first step for producing (meth)acrolein from the reactantssuch as propylene or the like and a second step for producing(meth)acrylic acid from the (meth)acrolein.

Moreover, the Mo—Bi—Nb based composite metal oxide according to thepresent invention may be used as a catalytic effective component of atleast one catalyst bed, when the reaction zone in which (meth)acrylicacid is produced using at least one reactant selected from the groupconsisting of propylene, propane, isobutylene, t-butyl alcohol andmethyl-t-butyl ether is packed with two or more catalyst beds.

When gas-phase catalytic oxidation is carried out by using the Mo—Bi—Nbbased composite metal oxide according to the present invention as acatalyst, there is no particular limitation in systems and operationconditions thereof used in the process. Reactors that may be used in thepresent invention include conventional fixed-bed, fluidized-bed, andmoving-bed reactors.

When the Mo—Bi—Nb based composite metal oxide according to the presentinvention is used as a catalyst for partial oxidation of propylene orthe like, (meth)acrylic acid can be produced by an one-step process,whereby (meth)acrylic acid can be produced using a fluidized bed reactoras illustrated in FIG. 1.

In this connection, catalyst particles and reactants flow into thefluidized bed reactor, and after reaction, they flow out of the reactor.Then, they are cooled and circulated through the reactor.

With reference to FIG. 1, the fluidized bed reactor will be described indetail.

A reaction gas containing propylene or the like is preheated to reactiontemperature in a heat exchanger 1, and the solid catalysts and reactiongas are mixed to pass through the fluidized bed reactor 2. The partialoxidation is generated in the reactor. Subsequently, non-reactants andproducts (e.g. acrylic acid) flow out of the reactor in a mixed state,and the solid catalysts and the produced gas are separated in a catalystseparator 3. The catalysts separated in the catalyst separator 3regenerate the inactivated catalysts in a catalyst regenerator 4, andfresh catalysts are supplied. Meanwhile, the produced gas separated inthe catalyst separator 3 is cooled to a temperature range forpurification in a plate-type heat exchanger 5, and then supplied in apurification process. At this time, the plate-type heat exchanger 5 canbe used for preheating a recycle gas.

In the fluidized bed reactor, since the particle size of catalyst issmall and fluidized, the amount of heat generated on the surface of thecatalyst particle can be minimized. Therefore, when (meth)acrylic acidis produced from propylene or the like in one-step process, instead oftwo-step process, the heat is not generated through two-step process,but simultaneously generated in one-step process, thereby causing aproblematic hotspot. Thus, in order to solve the problem due to thehotspot, the fluidized bed reactor is more preferable than fixed bedreactor.

Meanwhile, example of the fixed-bed reactor includes a sell and tubetype reactor, and the Mo—Bi—Nb based composite metal oxide of thepresent invention is packed into a reaction tube, and used as a fixedcatalyst bed for producing (meth)acrylic acid. For example, the reactionzone for producing (meth)acrylic acid from a reactant such as propyleneor the like can be packed with two or more of catalyst beds, and at thistime, at least one of catalyst bed, in which a catalytic effectivecomponent is Mo—Bi—Nb based composite metal oxide, can be used.

Reaction conditions, which are generally adopted for producing(meth)acrylic acid and (meth)acrolein from a reactant such as propyleneor the like via gas-phase catalytic oxidation, may be used. For example,a gas mixture as a starting material, which contains 4 vol % or more ofreactants such as propylene or the like, 10 to 20 vol % of molecularoxygen, and 60 to 80 vol % of inert gas functioning as a diluent (e.g.nitrogen, carbon dioxide, steam, or the like), is caused to be incontact with the catalyst according to the present invention, at atemperature of 250 to 50° C. 0 under a pressure of 0.1 to 3 kg/cm² Gwith a space velocity of 300 to 5000 hr-1 (STP) to carry out a desiredreaction.

(3) According to the present invention, (meth)acrylic acid can be stablyproduced with high yield for a long period of time, in which problemssuch as a hotspot problematic in a typical exothermic reaction, heataccumulation and a reduction in yield due to the hotspot can be solvedby controlling the activity of a catalyst containing Mo—Bi—Nb basedcomposite metal oxide and heat of catalytic reaction.

The catalytic activity can be controlled by the control of Nb/Mo ratio,catalyst calcination time, the amount of air supplied, and the catalystsize.

According to the present invention, (meth)acrylic acid can be producedby using the activity-controlled catalysts, in which the catalyst bedsin each tube in the shell and tube reactor are packed with various typesof catalysts in order to gradually increase their activity from inlet tooutlet.

That is, the reaction zone can be packed with two or more of differentcatalyst beds so that the particle size of the catalyst in the catalystbeds having a catalytic effective component of Mo—Bi—Nb based compositemetal oxide gradually decreases from the inlet, in which the reactantsare introduced, to the outlet, in which the reaction products areoutputted.

Mode for Invention

Hereinafter, the present invention will be described in detail withreference to Examples and Comparative Examples. However, these Examplesare for illustrative purposes only, and the invention is not intended tobe limited thereto.

CATALYST PREPARATION EXAMPLE Preparation Example 1 Catalyst 1

2500 ml of distilled water was heated and stirred at 70 to 85° C. and1000 g of ammonium molybdate was dissolved therein to form a solution 1.Then, 274 g of bismuth nitrate, 228 g of ferrous nitrate and 2.3 g ofpotassium nitrate were added to 400 ml of distilled water, the materialswere mixed thoroughly, 71 g of nitric acid was added thereto, and thematerials were dissolved sufficiently to form a solution 2. 686 g ofcobalt nitrate was dissolved in 200 ml of distilled water, so as to forma solution 3. After mixing the solution 2 with the solution 3, the mixedsolution was further mixed with the solution 1 while the temperature wasmaintained at 40 to 60° C., so as to provide a catalyst suspension.

The catalyst suspension was dried and the obtained cake-shaped solid waspulverized into a size of 150 μm or less. The resultant catalyst powderwas mixed with a predetermined amount of water for 2 hours, and formedinto a cylindrical shape. The catalyst was formed to have a diameter of5.0 mm and a height of 5.0 mm, and calcined at 500° C. for 5 hours underthe air, resulting in a catalyst 1. The produced catalyst had theelemental composition of except oxygen. The resulting catalyst had thefollowing elemental composition except oxygen:

Mo₁₂Bi_(1.2)Fe_(1.2)Co₅K_(0.05)

Preparation Example 2 Catalyst 2

Catalyst 2 was provided in the same manner as described in PreparationExample 1, except that 64 g of niobium chloride were further added toform a solution 1. The resulting catalyst had the following elementalcomposition except oxygen:

Mo₁₂Nb_(0.5)Bi_(1.2)Fe_(1.2)Co₅K_(0.05)

Preparation Example 3 Catalyst 3

Catalyst 3 was provided in the same manner as described in PreparationExample 1, except that 64 g of niobium chloride were further added toform a solution 1 and the molded catalyst was allowed to have a diameterof 7 mm and a height of 7 mm. The resulting catalyst had the followingelemental composition except oxygen:

Mo₁₂Nb_(0.5)Bi_(1.2)Fe_(1.2)Co₅K_(0.05)

Preparation Example 4 Catalyst 4

Catalyst 4 was provided in the same manner as described in PreparationExample 1, except that 32 g of niobium chloride were further added toform a solution 1. The resulting catalyst had the following elementalcomposition except oxygen:

Mo₁₂Nb_(0.25)Bi_(1.2)Fe_(1.2)Co₅K_(0.05)

Preparation Example 5 Catalyst 5

Catalyst 5 was provided in the same manner as described in PreparationExample 1, except that 32 g of niobium chloride were further added toform a solution 1 and the molded catalyst was allowed to have a diameterof 7 mm and a height of 7 mm. The resulting catalyst had the followingelemental composition except oxygen:

Mo₁₂Nb_(0.25)Bi_(1.2)Fe_(1.2)Co₅K_(0.05)

Example

<Catalyst Packing and Catalytic Activity Test>

To a 3 m stainless steel reactor having an inner diameter of 1 inch andheated with molten nitrate salt, alumina silica was packed to a heightof 150 mm as an inert material, and any one or a mixture of Catalysts 1to 5 prepared in Catalyst Preparation Examples 1 to 5 shown in Table 1was packed to have a height of 2800 mm, from the inlet of the reactiongas toward the outlet.

The oxidation was performed by introducing feed gas containing 7 vol %of propylene, 13 vol % of oxygen, 12 vol % of water steam, and 68 vol %of inert gas onto the catalyst with a space velocity of 1500 hr-1 (STP),at a reaction temperature of 320° C. under a reaction pressure of 0.7atm.

In Tables 1, conversion ratio of a reactant and yield are calculated,based on the following Mathematical Formulae 1 and 2.

Conversion ratio of propylene (%)=[(mole number of reactedpropylene)/(mole number of supplied propylene)]×100  [MathematicalFormula 1]

Yield (%) of acrylic acid=[(mole number of produced acrylic acid)/(molenumber of supplied propylene)]×100  [Mathematical Formula 2]

The experimental results of the Examples and Comparative Example areshown in the following Table 1.

TABLE 1 Conversion ratio Yield of propylene (%) (mole %) of SectionCatalyst packed 320° C. acrylic acid Comparative 1 Catalyst 1 (2800 mm)98.67 9.51 Example 1 Catalyst 2 (2800 mm) 92.21 67.40 Example 2 Catalyst3 (800 mm) + 91.44 72.65 Catalyst 2 (2000 mm) Example 3 Catalyst 5 (800mm) + 93.87 76.84 Catalyst 4 (2000 mm)

1-19. (canceled)
 20. A reactor for producing (meth)acrylic acid using atleast one reactant selected from the group consisting of propylene,propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, whereina Mo—Bi—Nb based composite metal oxide is used as a catalyst.
 21. Thereactor according to claim 20, wherein the reactor is a shell and tubetype reactor and the tube is packed with the Mo—Bi—Nb based compositemetal oxide catalyst.
 22. The reactor according to claim 21, wherein areaction zone of the tube in which (meth)acrylic acid is produced usingat least one reactant selected from the group consisting of propylene,propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether is packedwith two or more catalyst beds, and the Mo—Bi—Nb based composite metaloxide is used as a catalytic effective component of at least onecatalyst bed.
 23. The reactor according to claim 22, wherein thereaction zone is packed with two or more of catalyst beds havingdifferent catalytic activities in order to increase the catalyticactivity of the catalyst bed from the inlet, in which the reactants areintroduced, to the outlet, in which the reaction products are outputted,along its tubular axis.
 24. The reactor according to claim 21, whereinthe reaction zone of the tube is packed with two or more differentcatalyst beds so that the particle size of the catalyst in the catalystbeds having an effective component of Mo—Bi—Nb based composite metaloxide decreases from the inlet, in which the reactants are introduced,to the outlet, in which the reaction products are outputted, along itstubular axis.
 25. The reactor according to claim 23, wherein thereaction zone of the tube is packed with two or more different catalystbeds having an effective component of Mo—Bi—Nb based composite metaloxide and the different molar ratios of Nb to Mo ([Nb]/[Mo]) and thecatalytic activity of each of the catalyst beds increases from theinlet, in which the reactants are introduced, to the outlet, in whichthe reaction products are outputted, along its tubular axis.